Drive mechanism

ABSTRACT

An intermittent drive mechanism for use in machine tools has driving and driven members coupled by constant ratio gears. In one range of relative positions of the gears drive is not transmitted through the gears but instead is transmitted through a cam and cam follower. The cam is so shaped as to cause a gradual deceleration of the driven member to zero followed by a gradual acceleration up to the speed maintained by the constant ratio gears.

United States Patent 1 Reeve 1 Jan. 16, 1973 [54] DRIVE MECHANISMPrimary Examiner-Leonard H. Gerin [75] Inventor: John Edwin Reeve,London, En- Palmer Estabrook gland [73] Assignee: Thorn ElectricalIndustries Limited, [57] ABSTRACT London, England Filed p 13 1971 Anintermittent drive mechanism for use in machine Appl. No.: 179,823

Foreign Application Priority Data Sept. 16, 1970 Great Britain..44,3l6/70 U.S. Cl. ..74/393, 74/84, 74/425.5,

' 74/426 Int. Cl. ..Fl6h 35/02, Fl6h 1/16, F16h 27/04 Field of Search..74/424.5, 426, 393, 84

References Cited UNITED STATES PATENTS 8/1962 McDonald a al ..74/426 xtools has driving and driven members coupled by constant ratio gears. Inone range of relative positions of the gears drive is not transmittedthrough the gears but instead is transmitted through a cam and camfollower. The cam is so shaped as to cause a gradual deceleration of thedriven member to zero followed by a gradual acceleration up to the speedmaintained by the constant ratio gears.

8 Claims, 8 Drawing Figures DETAILED DESCRIPTIONYOF THE DRIVE MECHANISMBACKGROUND OF THE INVENTION 'mechanis'ms, are used in machine tools,packaging machines and other special purposev machines for effecting thetransfer of workpieces, or of apart of the machine, through a number ofpredetermined positions in sequence.

Conventionally a Geneva mechanism or a cam and follower system is usedwhere definite control of the indexing motion is necessary. Suchmechanisms must be large, and therefore costly, when used to index .aheavy mass through a large angle, because all the energy required forthis purpose must be transmitted during one revolution or less of thedriving member.

SUMMARY OF THE INVENTION An object of the invention is. to provide anindexing mechanism which is of exceedingly simpleconstruction and yetwhich is effective in operation.

The invention consists in a drive. mechanism which has a cam and camfollower coupled to respective ones of a driving member and a drivenmembenThe cam. follower engages with the cam when. the members arewithin a range of relative positions to transmit drive from the drivingmember to the driven member, and;

when the members are not withinsaid range drive is effectedthrough'constantratio gears. By appropriately shaping the cam, the drivemechanism can be constructed so as to cause the driven member. toexperience a predetermined acceleration, a constant speed (drive beingthrough the. constant ratio gears) and then a predetermineddeceleration.

Preferably the cam is on the driving member and the cam followers are onthe driven member. Conveniently the gears may comprise a first gear onthe. driving member anda second gearon the driven member:

which engages withthe firstgear but which has teeth :missingcorresponding to the said ranges .of 'positions where drive istransmitted through'the carrrand cam follower. r

BRIEF DESCRIPTION OF-THE'DRAWINGS 1 I FIG..3' shows an alternativecam-.for use in, the A mechanism of FIG. 1; U I

FIGS. 4, Sand 7 are plan views of three further FIGS. 6 and 8 are viewssimilar to FIG. 2 of the mechanisms of FIGS. 5 and 7 respectively.

EMBODIMENTS. p The mixed motion drive mechanism shownin-FIGS.

III-1 dexing mechanisms embodying the invention; and

. gagement with the spur gear 48. Again, the spur gear cal cam 14 and aworm or spiral pinion l6, and the drivenshaft 12 carries a worm wheel orspiral gear 18 for engagement with the worm or spiral pinion 16. As

" illustrated, two cam follower sets are attached to f worm wheel 18with the teeth missing, as at 24, corthe worm wheel 18 for engagementwith the cam 14. Each set in this context consists of two followers.

The cam track 22 of the cam 14 is of varying slope, i.e. at the-ends ofthe track drive is transmitted from the cam to the cam follower while atthe center of the track (the position illustrated in FIGS. 1 and 2) nodrive is transmitted. Thus on rotation of the cam 14 from one end of itstravel to the other at constant speed the cam follower set willexperience controlled deceleration to zero speed followed by controlledacceleration.

The speed attained by the driven member when the cam follower set 20reaches the end of the track 22 is maintained by the worm l6 engagingwith the worm wheel 18 as the follower 20 nears the end of the track22.'This constant speed ratio is maintained until the next cam. followerset 20 engages the cam 14.

' While the cam follower set 20 is in engagement with the cam 14 it isnecessary to disengage the constant ratio drive through the worm l6 andworm wheel 18. In the example illustrated this is achieved by formingthe gages with the cam.

- The cam track 22 is raised from the surface of the cam 14 and each camfollower set 20'includes two rollers 26' which engage respective sidesof thetrack 22. An' alternative arrangement is shown in FIG. 3, in whichthe cam track takes the form of a groove 30 and each' camfollower setconsists of a single roller 32 which runs in the groove.

The camof FIG. 3 can be readily modified as shown in FIG. 4to provide adrive mechanism of particularly responding to'the position where thecamfollower ensimple construction. Here, the outer surface of the cam.34 is' toothed to provide a-straight or globoidal worm which engageswith the worm wheel 18. A cam follower set 36 projects from the centerof the missing-tooth portion 24 in the worm wheel 18 and carries asingle roller 38 which engages the track 30 in the worm 34.

In theembodiment shown in FIGS. 5 and 6 the cam '14 is similar to thatof FIG. l. However, the worm 16 is I replaced by a :bevel gear 42 on theshaft 44. A spur pinion 46 is also fixed on the shaft 44 and engages aspur gear 48 mounted on the shaft 12 and which replaces the worm wheel18 of FIG. 1. The spur gear 48 carries-the cam followers '26'and alsohas a gap 24 PREFERRED 1 and Ztransmits drive from a driving, shaftrlfl'toa drivenshaft 12. The'driving shaft 10 carriesa cylindri-- wherethere are no teeth,in which earn follower are in engagement.

FIGS.7 and 8 show a further embodiment which employs a concave globoidalcam '50 which engages with a position the earn and camfollower set 52attached'to the spur gear 48 which is mounted on thedriven shaft 12."!heshaft 10 also carries-a spiral gear 54 which engages aspiralgear 56 on ashaft 44 which also carries a spur pinion 46 for en- 48 has agap'24where teeth are missing. and on rotation of the shaft lofrom theposition illustrated first the gear 48 is accelerated to constant speedby the cam 50,

whereupon the'pinion '46 engages the gear 48 and drive .istrans'mittedat constant'speed ratio; Whenthe gap 24 'againreaches thepinion 46thefollower 52 again engages :the cam decelerate the gear 48 to rest.

The arrangements illustrated enable an indexing cycle to occupy morethan one revolution of the driving member, thus saving space and cost.Furthermore, successive indexing cycles need not employ the same numberof revolutions.

I claim:

l. A drive mechanism, comprising:

a driving member;

a driven member;

a cam coupled to oneof said members;

a cam follower coupled to the other of said members for engagement withsaid cam when said members are within a range of relative positions totransmit drive from said driving member to said driven member; and

constant ratio gears connecting said driving and driven members whensaid members are not within said range of relative positions. I

2. A drive mechanism as claimed in claim 1, wherein said cam is shapedto provide a controlled acceleration prior to drive being effectedthrough said constant ratio gears and a controlled deceleration afterdrive from said constant ratio gears is discontinued.

3. A drive mechanism as claimed in claim 1, wherein said cam is on saiddriving member and said cam follower is on said driven member, and saidconstant ratio gears provide a decreased velocity ratio.

4. A drive mechanism as claimed in claim 1, wherein one of said constantratio gears has teeth missing as positions corresponding to said rangeof position where drive is transmitted through said cam and camfollower.

5. A drive mechanism as claimed in claim I, wherein said cam is formedin one of said constant ratio gears.

6. A drive mechanism as claimed in claim 1, wherein said constant ratiogears comprise a worm driven by said driving member and a worm wheeldriving said driven member.

7. A drive mechanism as claimed in claim 1, wherein said constant ratiogears comprise a pair of spur gears one of which is driven by saiddriving member and the other of which drives said driven member.

8. A drive mechanism as claimed in claim 1, having a plurality of camfollowers with corresponding ranges of relative positions.

1. A drive mechanism, comprising: a driving member; a driven member; acam coupled to one of said members; a cam follower coupled to the otherof said members for engagement with said cam when said members arewithin a range of relative positions to transmit drive from said drivingmember to said driven member; and constant ratio gears connecting saiddriving and driven members when said members are not within said rangeof relative positions.
 2. A drive mechanism as claimed in claim 1,wherein said cam is shaped to provide a controlled aCceleration prior todrive being effected through said constant ratio gears and a controlleddeceleration after drive from said constant ratio gears is discontinued.3. A drive mechanism as claimed in claim 1, wherein said cam is on saiddriving member and said cam follower is on said driven member, and saidconstant ratio gears provide a decreased velocity ratio.
 4. A drivemechanism as claimed in claim 1, wherein one of said constant ratiogears has teeth missing as positions corresponding to said range ofposition where drive is transmitted through said cam and cam follower.5. A drive mechanism as claimed in claim 1, wherein said cam is formedin one of said constant ratio gears.
 6. A drive mechanism as claimed inclaim 1, wherein said constant ratio gears comprise a worm driven bysaid driving member and a worm wheel driving said driven member.
 7. Adrive mechanism as claimed in claim 1, wherein said constant ratio gearscomprise a pair of spur gears one of which is driven by said drivingmember and the other of which drives said driven member.
 8. A drivemechanism as claimed in claim 1, having a plurality of cam followerswith corresponding ranges of relative positions.